Ferruginous Pygmy-Owl

Life History

Food

Until 1997, according to Proudfoot and Beasom, no comprehensive study had been performed to analyze the diet of Ferruginous Pygmy-Owls. They observed owls in Texas, analyzed prey remains, and took video footage from inside nest boxes in order to confirm or clarify anecdotal accounts of Ferruginous feeding habits. Their results indicate that Ferruginous Pygmy-Owls, at least in Texas, are generalist predators and do not depend on any particular species to fill their diet (Proudfoot and Beasom 1997). Analysis of prey remains indicate that their diet consists mainly of mammals (8.6%), other birds (10.5%), reptiles (22.5%), and insects (58%) (Proudfoot and Beasom 1997). They also observed instances of predation on the hispid cotton rat (Sigmodon hispidus) and Eastern Meadowlark (Sturnella magna), confirming anecdotal accounts of the birds taking prey items larger than themselves (Proudfoot and Beasom 1997). Still, Ferruginous Pygmy-Owls have been under observation for a long time, and the feeding habits among owls elsewhere in their distribution is similar (Flesch and Steidl 2010). For example, in Brazil Schubart et al. (1965) reported a variety of insects in the diet (orthopterans, beetles, termites of the genus Nasutitermes, odonates, Hymenoptera: Formicidae, and cicadas) as well as a rodent and small reptiles (several lizards, including a geckonid, Gymnodactyulus; and a snake). Among insects, the most common prey items are grasshoppers and crickets in the US, and also some scorpions in Mexico (Flesch and Steidl 2010; Proudfoot and Johnson 2000). Peak feeding occurs during the dawn and dusk. During the nesting season, owls forage mainly between 6:00 and 9:00, and between 20:00 and 22:00 (Proudfoot and Beasom 1997). Ears are symmetrical, which suggests that vision plays a more important role in the location and capture of prey items (Proudfoot and Johnson 2000). Ferruginous Pygmy-Owls perch at low heights and use short, swooping dives to catch prey once it has been found. Although adults capture prey in their talons, juveniles sometimes attempt to use their beaks. Killing prey usually consists of biting behind the neck to sever the spinal cord. Before consumption, many mammalian, avian, and insect species are decapitated. Avian species are also sometimes plucked, and their wings and tails are usually removed. Insects are often dissected to expose their softer parts; exoskeletons and other hard body parts are discarded. Smaller prey items (mostly insects) are consumed immediately upon capture, while larger prey may be cached for later consumption (Proudfoot and Johnson 2000). Proudfoot and Beasom (1997) observed owls in Texas using open cavities and patches of ball moss near their nests to store prey. Pellets are 19-25 mm and defecation occurs at habitual posts near nesting sites (Proudfoot and Johnson 2000).

Behavior

Ferruginous Pygmy-Owl perches and nest at short heights as low as 1 m above the ground but commonly between 4 and 6 m. Nests are built higher in the canopy during the nesting season until the fledgling stage (Proudfoot and Johnson 2000). They walk along or hop between branches and employ short direct flights to move larger distances. Adults use the bark of trees to clean their bills, and mating pairs have been known to preen each other (Proudfoot and Johnson 2000).

Territoriality

Males in Texas defend an area roughly 350-600 m in radius when involved in a pair bond (Proudfoot and Beasom 1996). The closest nests there were 741 m apart. In Arizona the territory can be as small as 150 m in radius. Unpaired males defend smaller territories between 100 to 150 m in radius (Proudfoot and Johnson 2000). Territories are claimed using territorial/advertisement calls (Flesch and Steidl 2007).

Sexual Behavior

Ferruginous Pygmy-Owls maintain strictly monogamous pair bonds. However paternity tests have not been conducted (Proudfoot and Johnson 2000) and no evidence is available (anecdotal or otherwise) on extra-pair matings. Males maintain pair bonds through territorial/advertisement calls and prey offerings. Females often reciprocate with "chitter" calls and copulation, which is often observed following prey offerings (Proudfoot and Beasom 1997) and lasts between 2 and 3 s (Proudfoot and Johnson 2000). The fact that copulation is also observed during and after incubation (Proudfoot and Johnson 2000) indicates that it plays a social role in the lives of Ferruginous Pygmy-Owls beyond reproduction. Pairs also preen and scratch each other.

Social and interspecific behavior

Ferruginous Pygmy-Owls are solitary or in pairs; never found in flocks. Young disperse about 8 weeks after the fledgling stage (Proudfoot and Johnson 2000). Coexists with other owl species, although the Ferruginous Pygmy-Owl may compete with Elf Owl (Micrathene whitneyi) and screech-owls (Megascops spp.) for food (Proudfoot and Johnson 2000). Ferruginous Pygmy-Owls sometimes nest close to the nests of other owl species, and they have been observed responding to vocalizations of other species of owl, such as of the Eastern Screech-Owl (Otus asio) and the Northern Saw-whet Owl (Aegolius acadicus; Proudfoot and Beasom 1996). When calling, is sometimes is mobbed by various passerines (Howell and Webb 1995, Hilty 2003, Proudfoot and Johnson 2000).

Predation

Raccoons (Procyon lotor) have been observed taking eggs in Texas and eating fledglings (Proudfoot and Johnson 2000). Snakes have been observed eating nestling, and based on analysis of nest remains they eat eggs as well. Fledglings and adults are consumed on occasion by Great Horned Owls (Bubo virginianus) and Cooper’s Hawks (Accipiter cooperii) (Proudfoot and Johnson 2000). When approached by potential threats, Ferruginous Pygmy-Owls assume an erect position (Santillan et al. 2008) and often move their tails vigorously. They may puff up their chests to erect their feathers (Proudfoot and Johnson 2000) and display small ear tufts (Santillan et al. 2008). Pairs often attack together, diving at predators and raking their talons. Observations by Proudfoot in Texas suggest that, although defense of eggs is rare, defense of nestlings is common and increases with advancement of developmental stage (Proudfoot and Johnson 2000).

Reproduction

Ferruginous Pygmy-Owls reproduce once annually, though they may nest a second time in the same season if the first attempt is unsuccessful (e.g. predation or disturbance occurs). Unpaired males observed in Texas and Arizona start broadcasting territorial/advertisement calls in February, and nesting commonly begins in April or May (Proudfoot and Johnson 2000) Ferruginous Pygmy-Owls are cavity nesters (Flesch and Steidl 2010) and select their nest sites sometime between the commencement of territorial/advertisement calls and the onset of nesting (Proudfoot and Johnson 2000). Pairs commonly use three cavities in the same area: one for nesting, one for storing prey, and one as a roosting post for the male (Proudfoot and Johnson 2000). Cavities are either naturally occurring in trees, stumps and cacti, or excavations made by woodpeckers (Flesch and Steidl 2010). Eggs are generally between 7 and 9 gr, white and unmarked (Proudfoot and Johnson 2000). Clutches contain between 2 and 5 eggs, laid between 32 and 39 hours apart (Proudfoot and Johnson 2000). Incubation typically lasts 23-28 days and is performed solely by the female; the male occupies himself foraging for prey, feeding the female, and staking the territory (Proudfoot and Johnson 2000; Proudfoot and Beasom 1997). Birds are born blind and altricial, requiring constant parental care upon hatching for up to 8 days (Proudfoot and Johnson 2000).

Populations and Demography

Little information is available regarding life span, survivorship, reproductive success and population density throughout the owl’s range. Populations have been shrinking in most of Arizona and Texas since the 1920’s (Flesch and Steidl 2006; Flesch and Steidl 2007; Johnson et al. 2003; Proudfoot et al. 2006b), particularly along the peripheries of habitation, and populations may be experiencing similar decline more recently in northern Mexico (Sonoma) (Flesch and Steidl 2006; Johnson et al. 2003; Flesch and Steidl 2010), although research is needed. Some data exist on current population densities in Arizona and Texas, but historical accounts of Ferruginous populations are dominated by anecdotal evidence, so the rates of population shrinkages are difficult to calculate. In 1999, 99 nests were recorded in Kennedy County, Texas, and 16 nests in the Tuscon Basin of Arizona (Proudfoot and Johnson 2000). Proudfoot et al. (2006) estimated the population size of all owls in Arizona at 13-117 individuals (Proudfoot et al. 2006). In the south of Mexico through its range in Central and South America, the species is considered common, although population estimates are unavailable. The main cause of mortality in fledgling and adult Ferruginous Pygmy-Owls is predation, most notably by raccoons (Procyon lotor), Great Horned Owls (Bubo virginianus), Cooper’s Hawks (Accipiter cooperii), Harris’s Hawks (Parabuteo unicinctus) and other mammalian and avian predators (Proudfoot and Johnson 2000). Starvation is also a documented cause but accounts for few deaths (Proudfoot and Johnson 2000). Several body parasites have also been identified in fledglings, but their overall affect on Ferruginous health is unknown. Among them are Philornis mimicola and Ornithodoros concanensis in Texas populations (Proudfoot et al. 2006), and Protocalliphora sialia and Hesperocimex sonorensis in Arizona (Proudfoot et al. 2005). Known health consequences include blood loss and anemia (Proudfoot et al. 2006). Ferruginous Pygmy-Owls court and nest in their first year (Proudfoot and Johnson 2000).